Home Secretary Theresa May withdrew an extradition order against the 46-year-old Brit on medical and human rights grounds in October. Five psychiatrists warned there was a risk McKinnon, who suffers from Asperger Syndrome and depression, would commit suicide rather than accept extradition to America.

US authorities had sought to secure the extradition McKinnon on trial to put him and jail him for accessing US military and NASA computers between 2001 and early 2002.

McKinnon, who lives in London, was arrested in March 2002 by officers from the UK's since disbanded Hi-Tech Crime Unit. His case was put on hold until US extradition proceedings began in 2005. McKinnon's family and his many supporters fought a fierce and ultimately successful campaign against extradition. The campaigners consistently argued that McKinnon ought to be tried in the UK, if anywhere.

Even after the threat of US extradition was lifted the possibility of a UK prosecution remained. CPS lawyers discussed with Met officers the possibility of launching a new prosecution against McKinnon in November. That option was rejected. He will not face further investigation nor a criminal prosecution in the UK, the CPS and MPS said in a joint statement on Friday:

Following discussions between the US Department of Justice, the police and the Crown Prosecution Service in the autumn of 2002, a decision was taken that the appropriate place for Mr McKinnon to be tried was the United States.

None of the reasons for the original decision in 2002 that the appropriate place for Mr McKinnon to be tried was the United States have altered. So far as the evidence is concerned, the position in 2012 is the same as it was in 2002. Most of the witnesses are in the US, as is nearly all the physical evidence and the bulk of the unused material, some of which is sensitive. Accordingly, in November this year, the CPS and the police met senior officials from the US Department of Justice to discuss the possibility of bringing the US witnesses to England and Wales for trial and of transferring all the US material to this jurisdiction to be considered.

The potential difficulties in bringing a case in England and Wales now should not be underestimated, not least the passage of time, the logistics of transferring sensitive evidence prepared for a court in the US to London for trial, the participation of US Government witnesses in the trial and the need to fully comply with the duties of disclosure imposed on the CPS. The prospects of a conviction against Mr McKinnon, which reflects the full extent of his alleged criminality, are not high.

After consulting with the Metropolitan Police Service and the CPS and having carefully considered matters, on 4 December this year, US authorities indicated to us that they would be willing to co-operate with a prosecution in England and Wales if that would serve the interests of justice.

However, they do not consider that making all the US witnesses available for trial in London and transferring all of the US material to this jurisdiction would be in the interests of justice given our representations and the reasons for the decision that the US was the appropriate forum as set out above. That is a decision the US authorities are fully entitled to reach and we respect their decision.

Against this background, the joint CPS/police panel recommended to the Assistant Commissioner of the Metropolitan Police that he should not commence a new criminal investigation into Mr McKinnon. The Assistant Commissioner of the Metropolitan Police has accepted that advice.

Karen Todner, McKinnon's solicitor, said: "The CPS state that the appropriate jurisdiction would be the United States, which is an interesting decision bearing in mind Mr McKinnon was arrested and interviewed by British Police in 2002.

"Mr McKinnon has always indicated that he would be willing to plead guilty to an offence under the Misuse of Computers Act but clearly cannot do so if he is not going to be prosecuted."

During McKinnon's fight against extradition, UK prosecutors consistently refused to take up the case, even when the McKinnon team offered CPS lawyers a signed confession.

The McKinnon case prompted changes to the US-UK extradition procedure. UK courts will soon be allowed to decide whether to assert jurisdiction over a case before processing an extradition request, a procedure known as a "forum bar". ®